1. The Field of the Invention
The present invention relates to medical devices. More specifically, the present invention relates to a method and apparatus for manufacturing endoprostheses, such as an expandable stent.
2. The Relevant Technology
Stents, grafts, and a variety of other endoprostheses are well known and used in interventional procedures, such as for treating aneurysms, for lining or repairing vessel walls, for filtering or controlling fluid flow, and for expanding or scaffolding occluded or collapsed vessels. Such endoprostheses can be delivered and used in virtually any accessible body lumen of a human or animal, and can be deployed by any of a variety of recognized means. One recognized indication of an endoprosthesis, such as a stent, is for the treatment of atherosclerotic stenosis in blood vessels. For example, after a patient undergoes a percutaneous transluminal coronary angioplasty or similar interventional procedure, a stent is often deployed at the treatment site to improve the results of the medical procedure and reduce the likelihood of restenosis. The stent is configured to scaffold or support the treated blood vessel; if desired, it can also be loaded with a beneficial agent so as to act as a delivery platform to reduce restenosis or the like.
An endoprosthesis, such as a stent, is typically delivered by a catheter delivery system to a desired location or deployment site inside a body lumen of a vessel or other tubular organ. It is useful for the endoprosthesis to be expandable, thereby enabling the endoprosthesis to be of a sufficient size to be introduced into a body lumen of a vessel and thereafter expanded to scaffold or support the treated vessel.
Expandable endoprostheses can be manufactured from a variety of materials and by a variety of methods. For example, a common material used in endoprostheses is a shape memory material (SMM), such as a shape memory alloy (SMA) or shape memory polymer (SMP). SMM is a suitable material due to its properties. SMM's can be “trained” to assume a certain shape after its shape has been deflected, as well as assume a certain shape at a given temperature range. SMM's can have a one-way characteristic, meaning the SMM has a single “trained” shape, or can have a two-way characteristic, meaning the SMM can have more than one “trained” shape. Two-way SMM's can assume different shapes at different temperature ranges.
An endoprosthesis made from a SMM can have advantages. For example, an endoprosthesis, such as a stent, can be manufactured from a piece of tubular SMM material having a diametrical size substantially equal to the desired non-expanded stent size. Thereafter, the unfinished stent can be stretched and “trained” to have a desired expanded orientation through a series of deformations, heating and cooling.
After the stent is “trained” and in the expanded orientation, it is necessary to collapse the stent down to its non-expanded orientation. This can be accomplished by a crimper mechanism with multiple jaws. The jaws of the crimper mechanism can be forced together when the expanded stent is positioned therebetween. As such, the jaws apply force to the expanded stent to collapse the stent. While a crimping mechanism with jaws can be successful in collapsing a stent, this crimping or collapsing process can introduce undesired point forces and surface shear stresses on the stent. Point forces and shear stress on the stent can introduce weaknesses in the stent and reduce the stent's performance and ability to effectively expand. Although the crimping mechanism is useful in collapsing the expanded stent to a non-expanded or collapsed orientation, there remains a need for a device which reduces point forces and shear stresses on stents during their manufacturing process.